Spinal stenosis typically occurs when the spinal cord, cauda equina and/or nerve root(s) are impinged by one or more tissues in the spine, such as a buckled or thickened ligamentum flavum, hypertrophied facet joints, disc herniations, etc. Impingement of neural and/or neurovascular tissue in the spine by hypertrophied facet joints, disc herniations, etc. may cause pain, numbness and/or loss of strength or mobility in one or both of a patient's lower limbs and/or of the patient's back.
In lumbar spinal stenosis (LSS), such as, for example, central lumbar stenosis or foraminal lumbar stenosis, the space around the spinal cord or nerve roots becomes narrow, thus compressing the spinal cord and the nerve roots. This causes back pain with neurogenic claudication, i.e., pain, numbness, or weakness in the legs that worsens with standing or walking and is alleviated with sitting or leaning forward. Compression of neural elements generally occurs as a result of hypertrophied facet or ligamentum flavum hypertrophy, disc herniations. LSS is one of the most common reasons for back surgery and the most common reason for lumbar spine surgery in adults over 65 years of age. Patients suffering from spinal stenosis are typically first treated with conservative approaches such as exercise therapy, analgesics, anti-inflammatory medications, and epidural steroid injections. When these conservative treatment options fail and symptoms are severe, surgery may be required to remove impinging tissue and decompress the impinged nerve tissue.
Decompressive laminectomy, a well-known treatment for LSS, unroofs the spinal canal by resectioning posterior spinal elements, such as the facet adjacent to the lumbar nerve roots. Wide muscular dissection and retraction is needed to achieve adequate surgical visualization. The extensive resection and injury to the posterior spine and supporting muscles can lead to instability with significant morbidity, both post-operatively and longer-term. Spinal fusion may be required to reduce the resultant instability. Laminectomy may be used for extensive multi-level decompression.
A combination of hemilaminotomy and laminotomy, often referred to as laminoforaminotomy, is less invasive than laminectomy. This procedure focuses on the interlaminar space in order to minimize resectioning of the stabilizing posterior spine. Generally, laminotomy removes the ligamentum flavuum. Muscular dissection and retraction are required to achieve adequate surgical visualization.
Microendoscopic decompressive laminotomy (MEDL) is somewhat similar to laminotomy, but utilizes endoscopic visualization. The position of a tubular working channel is confirmed by fluoroscopic guidance, and serial dilators (METRx™ lumbar endoscopic system, Medtronic) are used to dilate the musculature and expand the fascia. For MEDL, an endoscopic curette, rongeur, and drill are used for the laminotomy, facetectomy, and foraminotomy. The working channel may be repositioned from a single incision for multilevel and bilateral dissections.
Instruments have been developed for effectively cutting and coagulating organic tissue, which employ mechanical vibrations that are transmitted to a surgical end-effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to organic tissue at suitable energy levels, and using a suitable end-effector, such as a blade, may be used to cut, dissect, elevate or cauterize tissue or to separate muscle tissue from bone. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer, through a waveguide, to the surgical end-effector.
Activating or exciting the end-effector, for example, a cutting blade, at ultrasonic frequencies induces longitudinal vibratory movement. High frequency longitudinal or rotational, low amplitude virbrations are used for cutting which produce virtually no heat. The tools used are rated at between about 5 W to about 30 W to assure virtually no heat is produce.
Ultrasonic vibration is induced in the surgical blade by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end-effector or blade via an ultrasonic waveguide extending from the transducer section to the surgical end-effector. The waveguides and the end-effectors are designed to resonate at the same frequency as the transducer. Therefore, when an end-effector is attached to a transducer, the overall system frequency is the same frequency as the transducer itself. However, those skilled in the art will appreciate that the system may be designed where the transducer and the blade resonate at different frequencies and when joined the system resonates at a desired frequency.
Ultrasonic speeds and amplitudes are considered safe for dura material. However, performing spinal surgery, such as, for example, lateral lumbar spinal stenosis decompression (“open decompression”) using ultrasonic cutting devices can pose risks to healthy tissues and/or nerves, such as, for example, the lumbar nerve roots because of their cutting capabilities.
Accordingly, there is a need for devices and methods to provide efficient severing or cutting tissue including bone that can be used during a minimally invasive procedure and/or during an open surgical procedure, such as open decompression. Further, there is also a need for devices and methods that provide fine dissection capabilities of bone without damaging nerves. Devices and methods that do not cause a high level of collateral thermal damage and allow for the control of necrosis in the tissue being treated are also needed.